Electrodeposition of alloys



Aug. 8, 1933. R. M. BURNS ELECTRODEPOS ITION OF ALLOYS Filed March 30,1928 lNVENTUR RDBERT M BURNS A TTURNEK Patented Aug. 8, 1933 UNITEDSTATES 1,920,964 I ELECTRODEPOSITION OF ALLOYS Robert M. Burns,Brooklyn, N. Y., assignor to Bell Telephone Laboratories, Incorporated,.New York, N. Y., a Corporation of New York Application March 30, 1928.Serial No. 265,880

10 Claims.

, 5 cally deposit from a single electrolyte an alloy of three metalswhich will have a substantially uniform composition-throughout.

', A specific object is to deposit an alloy of iron, nickel, and cobaltupon a conductor in any one of a variety of proportions of these metalssuitable as a magnetic loading material.

It is generally known in the art of electrodepositing that if two metalsare to be electrodeposited simultaneously in definite proportions over aperiod of time, it is necessary that it be equally'easy for each metalto be deposited in its desired proportion. The ease with which ions of ametal in solution leave the solution and deposit 'on a cathode ismeasured by the drop of potential at the cathode for the particularsolution. If a solution contains ions of two metals in a givenproportion and it is desired to deposit them on a cathode-in thisproportion, then the potential of the cathode with respect to one of themetals in thesolution must be the same as the potential of this cathodewith respect to the other metal in solution. This is commonly difiicultto realize in practice. Thus, when depositing two metals that havesimilar cathode potentials such as copper and zinc out of a cyanidesolution as is normally done in brass plating, the instantaneous,

cathode potential of the copper in the solution may become diiierentfrom that of the zinc in the solution, resulting in a brass deposit thatis either copper-rich or zinc-rich and correspondingly copper-colored orelse more yellow-colored than the average brass deposit. There areseveral conditions in the electroplating process which may affect thepotential of a metal or metals in the solution with respect to thecathode. Such conditions are the concentration of the ions of the metalor metals in solution, the presence of other ions and substances in theelectrolyte, the temperature of the electrolyte and the current density.Some'of these conditions admit of regulation or control as doestemperature, proportion of different metal ions, or presence of othersubstances, but it is difficult, if not impossible, to maintain theaverage instantaneous current density in the electrolyte constant. Evenif this were possible the current density would still varyfor'dififerent points on the surface of' the cathode, depending on thedistance between the anode and various points on the cathode.-

characteristics of both metals coincide over a sub- When depositing twoor more metals simultaneously to obtain an alloy of the metals, thevaria-' tion in current density usually causes the cathode potential ofone of the metals to change in greater or lesser degree than the cathodepotential of the other metal or metals, thus varying the'composition ofthe alloy. Even when the rate of change of cathodepotential with respectto current density is the same for the two metals at equal cathodepotentials, it is found that, in depositing two metals simultaneously,the one having the lower cathode potential deposits ingreater proportionthan the other metal until the concentration of the ions of the firstmentioned metal is 'considerablyreduced, after which the second metalwill deposit in greater amounts. In accordance with U. S. Patent 1,837,355 granted to R. M.

Burns and C. M. Warner, on December 22, 1931, for given operatingconditions nickel and iron are deposited on a cathode as an alloy ofuniform composition and each metal is simultaneously de-, posited in itsproper proportion by varying the composition of the electrolyte untilthe rate of change of the current density-cathode potential stantialportion of the current density range. In this manner the -variation ofcathode potential with current density is the same for both nickel andiron in forming the alloy and consequently a deposit of uniformcomposition is obtained over the entire surface of the cathode, evenwith appreciable changes in the current density.

which has in solution nickel, iron and cobalt ions in quantitiesnecessary to produce an alloy of some desired composition. Theelectrolyte may be replenished during operations with the metals of thealloy by providing anodes of one, two or all the metals, together withtheir ions insoution, or by providing a single inert anode, max is, onewhich is noncorrosive in the electrolyte, and adding from time to timesuflicient ions in solution to replace those deposited at the cathode.The current furnished to the electrolyte is regulated according to the.alloy desired andif more than one anode is employed the current isapportioned through each. A smooth flexible alloy of any desiredthickness is thus obtained providing the acidity of the electrolyte ismaintained within certain narrow limits. In order to produce a brittlealloy, such as is required for making magnetic dust, the acidity orcurrent density, or both, may be increased. But the increase should notbe carried to such limits as to cause substantial change in thevariations of the cathode potentials of the metals deposited, otherwisetheproportions of the deposited constituents will be changed.Furthermore, by extending the time of electrodepositing and preparingthe surface of the cathode an alloy of sufficient thickness and strengthto allow for stripping from the cathode, may be formed. i

A feature of the invention'consists of asignaling conductor surroundedby a. magnetic alloy of nickel, ironand cobalt, electrolyticallydeposited thereon.

In the following description reference is made to two forms of apparatuswhich may be employed to electrodeposit an alloy of nickel, iron andcobalt. It is to be understood, however, that the invention is notlimited to these particular apparatus nor to the method of makingthisparticular alloy, herein described.

Referring to the drawing. Fig. 1 is a diagrammatic yiew of theelectrodepositing apparatus, with thefront of the tank removed, equippedwith anodes of the three metals to be deposited and adapted fordepositing the alloy in sheets, and Fig. 2 shows diagrammatically theapparatus adapted for producing the alloy as anadhesive coating on asignaling conductor. I

In Fig. 1 of the 'drawing the tank 10 contains an electrolyte 11, theanodes 12, 13 and 14 and the cathode 15. The battery 18 or othersuitable source supplies a positive potential to the anodes which may beelectrically connected, but means is preferably provided forindividually varying the potential applied to each anode so that thecurrents flowing therethrough may be adjusted to suitable values. Thecurrent flowing through each anode is preferably so adjusted that aconstant concentration of the ions of each metal is maintained in theelectrolyte and the anode areas are preferably such that the current perunit area is the same for each anode. When depositing anickel-iron-cobalt alloy composed of 40% nickel, iron and 25% cobalt,satisfactory results are obtained by employing anodes of nickel, cobaltand iron, respectively, having surface areas of to units, 25 to 28units, and 35 to 37 units, respectively, because of the differences inthe tendencies of these metals toward solution with normal metal ionconcentration. Because of the variations in corrosion eiiiciency of themetals employed as anodes, it may be preferable to provide anodes ofequal surface areas and correct for any corrosion inefficiency of themetals by adjusting the amount of current furnished to each anode.Instead of employing a plurality of anodes, one for each of the metalsto be deposited, a single anode composed of the alloy and havingsuitable proportions of the component metals may be employed where thealloy is desired in thin sheets. In cases where it may be advantageousto employ anodes of one or two of the components, salts, such as thehydroxides, of the remaining component metal or metals, may be addedcontinuously or at regular intervals so as to maintain the concentrationof the metal ions in the electrolyte substantially constant. Of thecomponent metals iron and cobalt are preferred for use as anodes intheorder mentioned, and

in such cases the nickel is added as a compound,

such as nickel hydroxides. If only one anode is employed iron isgenerally selected as the anode and then both the cobalt and nickel areadded in the form of hydroxides.

The cathode 15 may be of any suitable composition and form but where itis desired to strip the deposit from the cathode, it is preferable toemploy a flat cathode of a metal so treated that the deposited alloydoes not adhere firmly to it. When depositing nickel-iron-cobalt alloys,satisfactory results may be obtained by employing a cathode of brasswhich has been treated either by dipping in selenic acid or by coatingelectrolytically in a solution of ammonium molybdate. The adhesion ofthe deposited alloy to the cathode may also be prevented by coating thecathode with graphite. Another form of cathode which may be employed isa large slowly rotating cylinder having a portion of its surfacesubmerged in the electrolyte. The deposited alloy may then be removedfrom the cathode as it leaves the electrolyte and a continuous strip ofthe alloy may thus be obtained.

An electrolyte for producing an alloy of 40% nickel, 35% iron and 25%cobalt, may be made up from three separate electrolytes, each beingprepared as though the component metals are to be separately deposited.Each electrolyte is composed of the sulphate and the chloride of themetal it is prepared to deposit, together with a buffer mixture of boricacid and sodium sulphate, which mixture serves to maintain the acidityof the electrolytes constant over the operating range of currentdensity. The electrolytes are prepared as follows:

' Grams N0. 1 NiSO4.7H2O 210 NlClziSH-zO 30 H3303 25 Na2SO4 125 NO. 2FBSQi-VHZO 208 FeClzAHzO 30 1131303 25 Nazsoi 125 NO. 3 COSO4.7H2O 211COC12.6HeO Q 30 H3303 25 NazSOs 125 Suiiicient water is added to each ofthe above groups of constituents to make one litre of solution for eachelectrolyte and then the three electrolytes are mixed together inproportions of, No. 1: No.2: No. 3=4:3 /2:2 /2 to form an electrolytefor plating the alloy, composed of Grams NiSO4.7H2O 84 NiC12.6H2O 12resolnngo '13 FeClzAHzO 10.5 C0SO4.7H2O 53 COC12.6H2O 7.5

HaBOs 25 NazSO; 125

Where separate anodes such as 12, 13 and 14 representing nickel, ironand cobalt respectively, are employed in the plating electrolyte thecurrent is adjusted for each anode so that the metal ion concentrationin the electrolyte for the three metals, remains constant, and asatisfactory alloy composed of 40% nickel, 35% iron and 25% cobalt maythus be produced by'maintaining, first, the electrolyte at a.temperature of to C., secondly, the average of the instantaneous valuesof the current density at about 1.08 amperes per square decimeter, andthirdly, the hydrogen ion concentration (pH) of unnecessary because theelectrolyte is replenished with metal ions of the component metals byadding hydroxides of the metals in definite proportions directly to thesolution.

Nickel-iron-cobalt alloys of a wide range of compositions, particularlythose used for magnetic materials,.such as disclosed in the ElmerPatents 1,715,646 and 1,715,647, granted June 4, 1929 may be readilyobtained by varying the metal'ion concentration of the three metals insolution according to the proportions of the component metals in thealloy to be expected. The alloy may be made very brittle to facilitategrinding into dust such as is used in the manufacture of induction coilcores by increasing the acidity of the electrolyte or current density,or both, to a point where the plating potentials of the component metalsbegin to vary by substantial amounts with variations in currentdensities. It is well known in' the art that it is im'portant inproducing an alloy of uniform composition that the cathodepotential-current density characteristics of the component metals bemaintained substantially equal over the operating range of currentdensity.

Fig. 2 of the drawing illustrates diagrammatically a conductor 16 beingpassed slowly through a plating electrolyte 17, obtained as describedabove. of which it forms a cathode. That suitable rollers or other meansmay be provided for guiding the conductor through the electrolyte willbe understood. The conductor is connected to a source of current 18 bymeans of a roller contact 19. The anodes 20, 21 and 22 of nickel, ironand cobalt are also connected to the source of current 18. In thismanner an alloy of definite proportions may be satisfactorilyelectroplated on a signal conductor. The arrangement shown in Fig. 2 maybe varied to provide a single. inert anode or a separate anode for thethree component metais of the alloy as described above.

What is claimed is:

l. A method of simultaneously electrodepositing nickel, iron and cobaltto form a magnetic alloy of uniform composition which comprisesimmersing an electrical conductor as a cathode in a compositeelectrolytic bath consisting of separate electrolytic baths forelectrodepositing nickel, iron and cobalt mixed in proportions varyingin accordance with the relative percentages of the three metals desiredin the alloy, each of said electrolytic baths containing a solublesulphate and a soluble chloride of each of the metals to be depositedand a buffer mixture, passing a direct current of a value depending onthe alloy desired and the number of anodes employed in the compositebath through the composite electrolytic bath and cathode, andreplenishing said bath so that the concentration therein of the hydrogenion and the ions of each metal composing the alloy remain substantiallyconstant during operation to maintain the cathode potential-currentdensity characteristics of said metals substantially coincident over theoperating range' of current density.

2. A method, according to claim 1, wherein the step of replenishing theelectrolytic bath comprises adding iron as an anode in said bath.

3. A method, according to claim 1, wherein the step of replenishing theelectrolytic bath comprises adding iron and cobalt as anodes in saidbath. I

'4. A method according to claim 1, wherein the step of replenishing theelectrolytic bath comprises adding iron, cobalt and nickel as the anodesin said bath.

5. A method of simultaneously electrodeposit ing nickel, iron and cobaltto form an alloy of uniform composition which comprises immersing anelectrical conductor as a cathode in an electrolyte including solublesulphates and chlorides of said metals, which are mixed in proportionsvarying in accordance with the relative percentages of the three metalsin the alloy, a borate, and an alkaline metal, passing a direct currentof a value depending on the alloy desired and the number of anodesemployed in the composite bath through the electrolytic bath and cathodeand replenishing said bath so that-"the concentration therein of thehydrogen ion and the ions of the three metals composing the alloy remainsubstantially constant during the operation to maintain the cathodepotential-current density characteristics of said metals substantiallycoincident over the operating range of current density.

6. A method of simultaneously electrodepositing a uniformly composedmagnetic alloy of nickel, iron and cobalt in ranges of 10% to nickel,10% to 60% iron, and 5% to 80% cobalt, which comprises preparing asolution of soluble salts of the three metals selected in suchproportions as desired, from the group including sulphates andchlorides, passing through said solution to a cathode a direct currentwithin such ranges of current densities that the cathodepotential-current densitycharacteristics of the three metals aresubstantially coincident over the operating range of current density atthe surface of the cathode, and replenishing the ions of the threemetals at substantially the respective values of the three metals in thedeposited alloy.

7. The method of producing an alloy of approximately 40% nickel, 35%iron and 25% cobalt which consists in simultaneously electrodepositingthe three metals in the desired proportions from an electrolyte whichcontains per liter of water the following ingredients:

' Grams NiSO4.7H2O 84 NiClzfiI-IzO 12 FeSOrJlHzO 73 FeChAHsO 10.5COSO4.'7H2O 53' COC12.6H2O 7.5 H3303 25 Na2SO4 125,

and is subjected to such operating conditions as a temperature of 50 to60 C., an average instantaneous current density of 1.08 amperes persquare decimeter and a hydrogen ion concenequal over the operatingportion of the current density range.

9. In an apparatus for depositing an alloy of approximately 40% nickel,iron and 25% cobalt. an anodeof nickel, another anode of iron and still,another anode of cobalt, the surface areas of the anodes being 40 to 45%of nickel, to 37 of iron and 25to 28% of cobalt of the total anodeareas, and a cathode immersed in an electrolyte, and means for applyinga potential between said cathode and said anode, the composition of saidelectrolyte being such that the cathode potentials of the metalscomposing the alloy to be deposited are substantially equal over theyoperating range of current density.

10. In an apparatus for depositing an alloy of approximately 40% nickel,35% iron and 25% cobalt, a plurality of anodes comprising one of nickel,another of iron and another of cobalt, the ratio of the surface areas ofthe anodes being 40 to 45% nickel, 35 to 37% iron, and 25 to 28% cobalt,and a cathode immersed in an electrolyte which contains per liter ofwater the following ingredients:

. Grams NiSO-1.7H2O NiClz.6H2O 12 FeSO-a'IHzO 73 FeC12.4HzO 10.5C0SO4.6H2O 53 CoC12.6H2O 7.5 H3303 25 Na2SO4 125 ROBERT M BURNS.

